1. Field of the Invention
The invention relates in general to hydraulic elevators, and more specifically to new and improved arrangements for stopping an elevator car of a hydraulic elevator system at an upper travel limit.
2. Description of the Prior Art
The American National Standard Safety Code for hydraulic elevators, ANSI 17.1-1971, Section 302.2e, requires that the plunger of a hydraulic elevator system be provided with solid metal stops and/or other means to prevent the plunger from overtraveling beyond the limits of the cylinder, and the stops must be designed to stop the plunger at speeds up to 100 feet per minute in the up direction without damage to the hydraulic system. Direct metal to metal contact without cushioning between a stop ring on the plunger and a cylinder head part creates very high impact forces and thus a bulky and costly cylinder head is required.
Various approaches have been taken by the prior art to lessen the impact forces at the upper travel limit of a hydraulic elevator. For example, U.S. Pat. No. 963,905 allows the plunger and cylinder to separate to enable the fluid to escape the cylinder, while maintaining a mechanical connection between the plunger and cylinder. U.S. Pat. Nos. 244,092; 559,526; and, 531,792, teach hydraulic cushions which utilize chambers and sleeves which cooperate upon overtravel to provide a cushioned stop by virtue of tapers on the chamber walls and/or sleeve. U.S. Pat. No. 564,620 provides a hydraulic cushion by an auxiliary piston which enters an auxiliary fluid chamber and forces fluid through a series of openings which are progressively closed by the auxiliary piston as it traverses the auxiliary chamber. Still other prior art structures gradually cut off the supply fluid as the travel limit is reached, such as taught by U.S. Pat. No. 1,081,690.
While these prior art structures all provide a cushioned stop, it would be desirable to provide a new and improved upper travel limit stop for hydraulic elevators which is simple in structure, facilitating the manufacture and assembly thereof, and which provides a stop in which the retarding forces on the plunger may be programmed to stop the plunger and elevator car in a predetermined travel distance with reduced impact forces on the cylinder head, permitting the size and cost of the cylinder head to be substantially reduced.